1. Technical Field
The invention relates to a device for diverting surge currents or transient overvoltages and to the use of IGBTs as switching elements in a device for diverting surge currents or transient overvoltages.
Strong surge currents arise, e.g., in a direct lightning strike, due to induction caused by a lightning strike in the immediate environment, or upon starting a machine, or because of electrostatic charging.
These surge current create problems for a large number of electrical devices and appliances, which they may destroy.
2. Description of Related Art
Known devices for diverting surge currents or overvoltages are based on varistors and/or gaseous diverters and/or spark gaps, each in combination with a thermal separator. With respect to its function in a surge protector, each of these components has a different area of application, with corresponding advantages and disadvantages.
Depending on the purpose to which they are applied, these devices are also generally known as lightning strike diverters, overvoltage diverters, and overvoltage protectors, or (in English) surge protective devices (SPD).
The surge currents that arise during the different events are typically designated in relation to a characteristic form taken by the surge current. In testing and certification a distinction is made between a so-called 10/350 μs surge current (referred to below as 10/350 μs), which is characteristic for lightning current, and an 8/20 μs surge current (referred to below as 8/20 μs), which is characteristic for the other cases.
These surge current pulses are standardized and reproduced by way of example in FIGS. 1 and 2. In FIG. 2, the area beneath the curves provides a measure for the diverted energy.
Depending on their intended purpose, protective devices are tested using the appropriate test pulses and are divided into protective classes.
This division into classes or types permits a classification according to the surge current carrying capacity. Here type 1 diverters have a very high carrying capacity, and, in corresponding fashion, type 2 and 3 diverters have a lower carrying capacity.
In the known devices a strong diverted current can result in the destruction of the protective device.